No highway power

If the car losses power at 70 miles an hour I would check fuel volume and pressure.Tee in a fuel pressure gauge and tape the fuel pressure gauge to the windscreen and drive the car noting the fuel pressure when the car looses power. Check the fuel pressure volume it should be a pint in ten seconds. A restiction in the exhaust could do the same thing.

If you have a cold air intake, the cone air filter can mess with the way the air flows over the mass airflow sensor at high speeds. To rid this problem ive heard to place a couple pieces of duct tape across the cone filter on the bottom to make the air flow differently into the intake.